NFL players will be required to provide blood samples during training camp physicals for a study on human growth hormone, according to emails the players' association sent to its members that were obtained by USA TODAY Sports.

The population study will be used to determine what a "normal" HGH level is for an NFL player as negotiations continue on several other issues, including discipline for those caught with increased HGH levels, before testing is implemented across the league.

"I don't think it's a big issue," said Kansas City Chiefs offensive lineman Geoff Schwartz. "The testing is just to establish baselines. We agreed to testing in the CBA and this is the first step in that process."

Experts criticized the population study as another stall tactic by the union.

"There's an assumption here that they're (NFL players) somehow unique. Therefore, their HGH level would be different. I don't know why they came up with that, where they came up with that," said Dr. Gary Wadler, an internist, international sports doping expert and clinical associate professor of medicine at Hofstra North Shore-LIJ School of Medicine.

"It's just an opportunity to delay. I think that delay is detrimental to the sport," he added.

The union has said its players might have a higher natural HGH level than the general population — an assertion anti-doping experts have said is baseless — and balked at testing procedures approved by the World Anti-Doping Agency that the league recommended.

"The blood sample from each player will immediately be sent to the laboratory for analysis only for the purpose of the HGH population study; no other use will be made of any blood sample," the union said in an email to players dated July 12.

"After the laboratory has processed all player blood samples, the scientists will perform the calculations and analysis necessary to determine the proper decision limit for NFL players."

A list of training camp guidelines distributed by the NFLPA to players includes a note on the Day 1 schedule: "Physicals to include blood draw for HGH population study."

Another email features a Q&A that includes the passage: "The current stalemate regarding HGH testing and the League office is about whether the NFL, and others working with them, can force the Players to accept an unfair testing and discipline protocol when the collective bargaining process requires mutual agreement by both the Players and the NFL."

An NFLPA spokesman said he would consult with the union's legal team before commenting.

"We are in active discussions with the NFLPA regarding the implementation of HGH testing for NFL players," NFL spokesman Greg Aiello said in a statement to USA TODAY Sports. " Those discussions are focused on a full resolution of any remaining issues, including the role of a population study."

Former NFL player and head coach Herman Edwards believes the debate might be a smokescreen.

"You can test me any day you want, 'Wake me up at 2 in the morning, or 1 o'clock in the afternoon, it doesn't matter to me," Edwards said. "I'll come out fine.

"Unless you have something to hide, why are you worried about the test? Players say, "Well, we have to be prepared. You have to let us know.' Why do they have to let you know?''

The NFLPA first proposed a population study as part of "a comprehensive HGH testing program" in November 2011, four months after an agreement to begin testing for HGH was included in the collective-bargaining agreement.

Adolpho Birch, the NFL's senior vice president of labor policy and government affairs, sent a letter to the union on Jan. 10 saying the league no longer was interested in the population study after the sides had sparred over which doctor would conduct it.

According to the union's July 12 email, Dr. Alan Rogol has been jointly hired by the NFLPA and the NFL to oversee the study and supervise two jointly retained biostatisticians, including Donald Berry, who will design the study and analyze the results, with a second biostatistician to independently review the study protocol and the analysis.

"This is the scientific analysis to determine the appropriate decision limits for our Members that we have insisted upon since the signing of the CBA," the union's email said.

Anti-doping experts have said there was no need for a separate population study for NFL players because tests performed by the WADA before the HGH test was brought to market included scores of samples from football players and others with similar body types.

The union's July 12 email said there are "several additional issues which must be collectively bargained to agreement before final implementation of the hGH and Performance Enhancing Substances drug policy. One of those issues is the issue of discipline. The parties continue to discuss the issue and when a final proposal is reached, we will bring it to you for your review and vote."

Article 39, Section 7 of the collective-bargaining agreement finalized in July 2011 stated the league's performance-enhancing drug policy would include "both annual blood testing and random blood testing for human growth hormone," with discipline at the same level as steroid use. The deal provided for a timeline of several weeks to hammer out details on collection, transportation and testing of samples, but the process has gone far slower than that.

In October 2011, NFL commissioner Roger Goodell sent a letter to leaders of a congressional committee outlining the league's plans for collecting and saving blood samples of players. In the letter to California Rep. Darrell Issa and Maryland Rep. Elijah Cummings of the House Committee on Oversight and Government Control, Goodell said specimens would not be analyzed and players would not be subject to disciplinary proceedings until remaining issues about the testing regimen are resolved. Until that time, blood samples would be stored.

But no samples were taken.

That same month, nearly two dozen scientists and lab directors from around the world signed a letter sent to the NFL and the union stating the current test for HGH is safe, scientifically reliable and appropriate for use in professional sports leagues.

In November 2011, the league said the union's proposal was "deficient in numerous respects and consistent with the NFLPA's ongoing strategy to delay testing as long as possible."

NFL agent Alan Herman believes the testing, when finally implemented by the NFL, will have a trickle-down benefit.

"I think it will filter to the college level and maybe college will adapt it as well," he said. "Certainly, in the pro game, everybody will be on an even playing field. I'm not sure that exists right now."